The mechanical stabilization of soil slopes by means of plant roots depends largely on the strength properties of the roots and their growth pattern within the soil.In particular area, the selection of indigenous plant species on the basis of their root properties is an essential part of biotechnical slope protection. In order to examine the effects of shrub roots on slope stabilization in the geological hazards of landslide/debris flow, the mountainous region in Qinyuan county, south of Zhejiang, three species (Loropetalum chinense, Rhododendron latoucheae, Dalbergia millettii) were studied, which were dominant shrubs in midsubtropical evergreen broadleaved forest. The results showed that plant roots had positive effects on shear strength of topsoil (≤15mm), and have obvious different in both tensile stress and tensile strength. In the topsoil, the shrub L. chinense and R. latoucheae have more fibrous root than that of D. millettii, in quantity, so that D. millettii provided the minimum value of shear strength. The values of root tensile resistance increased with the increase in root diameter, following a power law equation, and the relationship between which was significant positively correlated. The power root tensile strength root diameter relationships depend on plant species. The root tensile strength of L. chinense and R. latoucheae decreased with increasing root diameter, following a power law equation and a negative correlation. However tensile strength root diameter relationships within D. millettii did not follow a power law equation. The fine root is better than the coarse root in contributing to stabilize sloping terrain and increasing the value of shear strength within topsoil.
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